1. Field of the Invention
This invention is in the field of microcalorimeter methods and devices.
2. Description of the Related Art
Essentially all chemical and biological reactions either release heat to the surrounding environment, or alternatively absorb heat from the surrounding environment. Thus devices and methods that can precisely perform thermodynamic measurements to determine this heat release or heat absorption are useful for obtaining more information about these reactions.
Although chemical reactions can often result in the release of large amounts of heat to the environment or absorption of large amounts of heat from the environment, biological reactions are often considerably more subtle. This is because many biological reactions of interest involve large molecules, which on a molar level are present in comparatively low amounts in typical samples. Additionally, because the binding forces involved often are comparatively weak, generally only small amounts of heat is generated or absorbed per molecular interaction. Biological molecules also tend to be difficult to obtain, and thus typically only small quantities are available for analysis. As a result, there was and is a need for ever more sensitive calorimeters, in particular microcalorimeters which can accurately measure the thermodynamic properties of such subtle interactions.
One of the problems that impacts all calorimeter designs is that the surrounding mass and heat capacity of the calorimeter instrument itself (usually referred to as the device addenda) tend to interfere with and degrade the various sample thermodynamic measurements. Thus as a general rule for this field, the smaller the amount of addenda (relative to the sample of interest) the better.
Denlinger et. al., in the article, “Thin film microcalorimeter for heat capacity measurements from 1.5 to 800K”, Review of Scientific Instrumentation 65(4), April 1994, pages 946-959 disclosed the utility of using thin films (membranes), composed of materials such as amorphous silicon nitride, as the basis substrate for producing improved microcalorimeters. Here the very thin sample supporting membrane provides a very small amount of addenda relative to the sample size, and this in turn allows for a more sensitive device.
In a further improvement of the thin film membrane method, in patent application Ser. No. 09/336,668 (since issued as U.S. Pat. No. 6,193,413), “System and method for an improved calorimeter for determining thermodynamic properties of chemical and biological reactions”, the contents of which are incorporated herein by reference, the present inventor described a novel system and method for an improved calorimeter for determining thermodynamic properties of biological and chemical reactions. The inventor's earlier application disclosed a sandwich-like microcalorimeter system formed from two thin amorphous membranes, each anchored to frames which could move relative to each other. In this system, usually thermometers and heaters were placed on one side of a thermal conduction layer mounted on the central portion of each membrane, forming two microcalorimeters, and the membranes and their supporting frames were then placed in a humidified environmental chamber.
According to the methods of application Ser. No. 09/336,668, two samples (first and second samples, often aqueous samples of sub-milliliter volume), are placed on the membranes of the two microcalorimeters. The heaters on each membrane heat the two samples, and the attached thermometers or temperature sensors then determine the heat capacity of each sample. The samples are then mixed by sandwiching the two microcalorimeters, and this mixing in turn causes a binding reaction to occur. The '668 system could also determine the enthalpy of the binding reaction by measuring the amount of heat liberated. The Ser. No. 09/336,668 system would then determine the heat capacity of the mixed sample by using the heaters to again heat the mixed sample, and again measure the temperature change of the sample using the temperature sensors. Various methods of using this data to determine a molecular binding constant were also disclosed.
Although the system and method of Ser. No. 09/336,668 thus represented an improvement over earlier microcalorimetric methods, there remains a need for ever more sensitive and more accurate microcalorimetric systems and methods.